* The $TRAVIS_COMMIT_RANGE could be not existed, because the git history
  can be changed and rebased. Here we alway run Travis-CI when `git diff`
  cannot return the modified files.
* Also do not push docs update if is not PaddlePaddle/Paddle.

- Put the 'ARG DEBIAN_FRONTEND=noninteractive' ahead of the first
  'apt-get install' invoke.
- Add comments to Dockerfiles to explain why we're adding Bazel
  installation.
Signed-off-by: NLi Peng <lipeng@unisound.com>

Also add DEBIAN_FRONTEND=noninteractive to suppress the debconf
messages.

* error when paddle has a wrong version number.

* Mount local Paddle instead of git clone from remote.
* Use official chinese ubuntu source instead of 163 mirror.

* Check all files by pre commit hooks

* Because in dockerhub, we cannot set the `docker build `running
  directory, we could only use `git clone` command to get the latest
  code if we put `Dockerfile` in subdirectory

* But the `git clone` will checkout the default branch only, so here
  we add a `ENV` in Dockerfile to checkout special branch or tag in
  git repo. We could change it to `V0.9.0` tag when it release.

* Init

* Add numpy deps

* Refine

For multiple installation of paddle, there might be multiple versions of python package at opt/paddle/share/wheels/. We should install the right version.
Ideally, we should remove the wrong versions when install. But it's not easy to do this with cmake.

Change-Id: Ida8a8d60643ad9e42cf1c85776de9122d5ba1392